A common class of experiments, known as a multiplexed assay or multiplexed bio-chemical experiment, comprises mixing (or reacting) a labeled target analyte or sample (which may have known or unknown properties or sequences) with a set of “probe” or reference substances (which also may have known or unknown properties or sequences). Multiplexing allows many properties of the target analyte to be probed or evaluated simultaneously (i.e., in parallel). For example, in a gene expression assay, the “target” analyte, usually an unknown sequence of DNA, is labeled with a fluorescent molecule to form the labeled analyte. One known type of assay is a “bead-based” assay where the probe molecules are attached to beads or particles.
For example, in a known DNA/genomic bead-based assay, each probe consists of known DNA sequences of a predetermined length, which are attached to a labeled (or encoded) bead or particle. When a labeled “target” analyte (in this case, a DNA sequence) is mixed with the probes, segments of the labeled target analyte will selectively bind to complementary segments of the DNA sequence of the known probe. The known probes are then spatially separated and examined for fluorescence. The beads that fluoresce indicate that the DNA sequence strands of the target analyte have attached or hybridized to the complementary DNA on that bead. The DNA sequences in the target analyte can then be determined by knowing the complementary DNA (or cDNA) sequence of each known probe to which the labeled target is attached. In addition, the level of fluorescence is indicative of how many of the target molecules hybridized (or attached) to the probe molecules for a given bead. As is known, a similar bead-based assay may be performed with any set of know and unknown molecules/analyte/ligand.
In such bead-based assays, the probes are allowed to mix without any specific spatial position, which is often called the “random bead assay” approach. In addition, the probes are attached to a bead so they are free to move (usually in a liquid medium). Further, this approach requires that each bead or probe be individually identifiable or encoded. In addition, a bead based assay has the known advantage that the analyte reaction can be performed in a liquid/solution by conventional wet-chemistry techniques, which gives the probes a better opportunity to interact with the analyte than other assay techniques, such as a known planar microarray assay format.
There are many bead/substrate types that can be used for tagging or otherwise uniquely identifying individual beads with attached probes. Known methods include using polystyrene latex spheres that are colored or fluorescent labeled. Other methods include using small plastic particles with a conventional bar code applied, or a small container having a solid support material and a radio-frequency (RF) tag. Such existing beads/substrates used for uniquely identifying the probes, however, may be large in size, have a limited number of identifiable codes, and/or made of a material not suitable to harsh environmental conditions, such as, harsh temperature, pressure, chemical, nuclear and/or electromagnetic environments.
Therefore, it would be desirable to provide encoded beads, particles or substrates for use in bead-based assays that are very small, capable of providing a large number of unique codes (e.g., greater than 1 million codes), and/or have codes which are resistant to harsh environments and to provide a reader for reading the code and/or the fluorescent label attached to the beads.
Also, there are many industries and applications where it is desirable to uniquely label or identify items, such as large or small objects, plants, and/or animals for sorting, tracking, identification, verification, authentication, or for other purposes. Existing technologies, such as bar codes, electronic microchips/transponders, radio-frequency identification (RFID), and fluorescence (or other optical techniques), are often inadequate. For example, existing technologies may be too large for certain applications, may not provide enough different codes, cannot be made flexible or bendable, or cannot withstand harsh environments, such as, harsh temperature, pressure, chemical, nuclear and/or electromagnetic environments.
Therefore, it would be desirable to obtain a labeling technique and/or encoded substrate for labeling items that provides the capability of providing many codes (e.g., greater than 1 million codes), that can be made very small (depending on the application) and/or that can withstand harsh environments and to provide a reader for reading the code and/or the fluorescent label attached to the beads.